1. Field of the Invention
This invention relates to battery separators, and in particular relates to forming a microporous separator envelope about a battery plate, such that the envelope functions as a battery separator for use in a lead-acid battery of the type, for example, used in automobiles.
2. Description of the Prior Art
In the prior art, it has been thought desirable to form a battery separator directly on the battery plate by a method of dipping the plate in one or more solutions. While prior art patents speak of such a process, in fact this desire has not been achieved in commercial practice.
To prevent the positive and negatively charged plates or electrodes of lead-acid batteries from coming into contact with each other, and thereby self-discharging the battery plates, sheets of separator material are positioned between the positive and negative battery plates. This separator material is usually comprised of pre-formed separator sheets which must be positioned either mechanically or manually between the positive and negative electrodes or sealed on three sides about one of the plate types, thereby enveloping them. In today's world of high-speed mass production, these techniques are slow, labor intensive, and most importantly generate large scrap rate losses when automated, and an inefficient process in the manufacture of batteries.
The present invention overcomes this necessity of enveloping the plates with separator material by mechanical process or positioning separator material between the plates. A separator envelop is produced simply by dipping the plate.
Prior patents have approached the idea of dipping or applying a coating on a battery plate. For example, see U.S. Pat. Nos. 756,176 (Mar. 29, 1904), 760,897 (May 24, 1904), 779,553 (Jan. 10, 1905), 994,451 (June 6, 1911), 1,141,251 (June 1, 1915), 1,316,597 (Sept. 23, 1919), 1,433,017 (Oct. 24, 1922), 1,725,734 (Aug. 20, 1929), 2,184,373 (Dec. 26, 1939), 2,256,105 (Sept. 16, 1941), 2,422,130 (June 10, 1947), 2,673,230 (Mar. 23, 1954), 2,759,039 (Aug. 14, 1956), 2,845,469 (July 29, 1958), 3,023,261 (Feb. 27, 1962), 3,035,110 (May 15, 1962), 3,542,596 (Nov. 24, 1970), 3,625,770 (Dec. 7, 1971), 3,265,771 (Dec. 7, 1971), 4,232,100 (Nov. 4, 1980); British Pat. Nos. 1890 (Nov. 30, 1901) and 274,208 (July 19, 1927); and Canadian Pat. No. 664,290 (June 4, 1963).
Other separator art patents include U.S. Pat. Nos. 364,344 (June 7, 1887), 2,569,361 (Sept. 25, 1951), 2,772,322 (Nov. 27, 1956), 3,766,106 (Oct. 16, 1973) and 4,251,605 (Feb. 17, 1981).
For the past four years, I have been experimenting largely without success, on methods of dip coating plates to form a commercially acceptable separator thereabout. I tested the disclosures of a number of patents to determine their worth as a practiced matter.
U.S. Pat. No. 2,845,469 (July 29, 1958) discloses the dipping of battery plates ostensibly to form a separator layer directly on the plate. That patent describes the formation of a layer on the outer surfaces of groups of battery plates by withdrawing the plate groups from a specific solution through a comb structure. The separator material and the dipping method disclosed therein do not provide a separator material nor a process for the formation of a separator material on a plate which would be suitable for a commercially useful lead-acid battery.
In evaluating this patent, I chopped ten grams of spun glass into one-quarter inch sections and placed the glass in a high shear mixer with 400 grams of water and shredded it for three minutes. I then blended in 20 grams of Kieselguhr (TLC Grade Baker analyzed), followed by 20 grams of lignin (that is, treated sawdust according to U.S. Pat. No. 2,882,331) followed by 20 grams of dry wheat paste. Finally, I added 4 grams of phenolic resin used by Evan's Products, Paper Separator Division for the production of their current commercial paper separators. All of this was blended until uniform in consistency.
A formed negative plate, that is an electrode, was dipped repeatedly into this solution to try to achieve a coating. I noted that no substantial coating would stick to the plate.
Nonetheless, following the teachings of the '469 patent, the plate was allowed to air dry and was baked at 340.degree. F. for five minutes as described in U.S. Pat. No. 2,882,331 to cure the resin properly. The coated plate was photographed as shown in prior art FIG. 1.
I noted that it had no separator and no envelope had been formed about the plate.
I had chosen these ingredients because they were described in the patent and appeared to be the best combination using the patent descriptions.
I also tested the disclosure of this patent using the following formulation:
200 grams wheat flour PA0 4000 grams water PA0 200 grams Hi-Sil-233(finely divided silica SiO.sub.2) PA0 200 grams ammonium lignosulfate PA0 100 grams chopped (1/4 inch) glass fiber PA0 40 grams CASCO resin (5H) (Urea Formaldehyde made Bordens Chemical) PA0 A. Cane Sugar, 150 grams; Water, 850 ml. Light Syrup. PA0 B. Cane Sugar, 500 grams; Water, 500 ml. Medium Syrup. PA0 C. Cane Sugar, 667 grams; Water, 333 ml. Heavy Syrup. (Saturated Sugar Solution) PA0 D. Cellulose Acetate, 30 grams; Tetrahydrofuran, 200 ml. PA0 E. Cellulose Acetatebutyrate, 60 grams; Tetrahydrofuran, 200 ml. PA0 F. Cellulose Acetate, 30 grams; Methylethylketone, 200 ml. PA0 G. Cellulose Acetate Butyrate, 60 grams; Methylethylketone, 200 ml.
These ingredients were combined as directed by '469 patent.
The coating suspension was not thick enough to coat a battery plate as disclosed. In fact, when only half the required amount of water was added, the coating suspension still would not coat the plate. In an effort to obtain a coating on the plate, the formulation was heated to make the wheat flour thicken the formulation (like gravy) and still the formulation would not thicken enough to yield a coating suspension capable of coating the plate in one dip.
Since the coating suspension was not thick enough to obtain a coating on the plate after one dipping, the plates were subsequently dipped into the suspension and air dried repeatedly. After the material had been applied by repeated dipping and drying, the plates were allowed to air dry for one day and then were soaked in battery acid for one day. The soaking of the plates resulted in the coating falling off the plates and being dissolved.
In an attempt to obtain a coating similar, though not identical, to that disclosed in the patent and enhance its ability to remain in place on the plate, a mixture comprising 50 grams of resin (rather than 40 grams) and 25 grams Hi-Sil-233 (rather than 200 grams) was made. The plates were dipped into this mixture and immediately set up in water. However, the coating material again dissolved after 24 hours in the acid. From this experiment, it would seem that the use of Urea Formaldehyde was unacceptable for creating a battery separator or envelop. Furthermore, the formulation disclosed is not suitable for dip coating a battery plate in order to form a battery separtor on the battery plate or an envelop about the plate.
U.S. Pat. No. 4,251,605 discloses a acrylonitrile porous polymer membrane and a process for making it.
Two approaches to the Inoue patent were taken:
(1) 50 grams of polyacrylonitrile-methylacrylate 94:6 copolymer, by Polysciences was dissolved in 250 grams of dimethylformamide (DMF) to form a solution. The solution was cooled down to zero degrees C. with ice. A 50/50 DMF water solution was also cooled down to zero.
A negative electrode was dipped in the cold polymer solution for three minutes. Bubbles appeared upon dipping the plate into the solution. Then the coated plate was immersed in the cold DMF water solution to coagulate the film for 15 minutes. Then the plate was washed in room temperature water for 30 minutes followed by three minutes immersion in a 85 degree C. hot-water bath, and then finally allowed to air dry. A photograph was taken (prior art FIG. 2). This plate was cycled and, compared with a control separator, a commercial paper separator of an inexpensive grade. The results of that test are as follows:
TABLE 1 __________________________________________________________________________ INITIAL VOLTAGE FINAL VOLTAGE INITIAL AMPERAGE FINAL AMPERAGE CYCLE # CYCLE # CYCLE # CYCLE # PLATE # 1 2 3 1 2 3 1 2 3 1 2 3 __________________________________________________________________________ CA (INOUE) 0.0 1.30 1.25 0.0 0.55 0.75 0 36 34 0 14 22 CONTROL 1.32 1.45 1.40 0.75 0.85 0.77 37 40 42 20 24 26 __________________________________________________________________________
These figures show inferior cranking performance.
A physical inspection of the material shows that it adhered to the surface of the plate, rather than formed an envelop and that it had unacceptable levels of pinholes clearly visable in prior art FIG. 2.
It will be noted that in conducting this test, I did not use the nitric acid suggested by the patentee, because the acid would have reacted with the plate and generated large amounts of hydrogen gas bubbles which would have increased the number of pinholes.
I conducted a further test on this patent's disclosure, based on the best example which had the best listed separator properties, as follows:
(2) 50 grams of polyacrylonitrile-methylacrylate 94:6 copolymer, by Polysciences was dissolved in 250 grams of 70% nitric acid to form a solution. The solution was cooled down to zero degrees C., with ice. A 40% nitric acid solution was also cooled down to zero.
A negative electrode was dipped in the cold polymer solution for three minutes. Bubbles appeared upon dipping the plate into the solution. Then the coated plate was immersed in the cold 40% nitric acid solution to coagulate film for 15 minutes. Then the plate was washed in room temperature water for 30 minutes followed by three minutes immersion at 85 degrees C. hot water bath and then finally allowed to air dry. The plate is identified as Plate CB in prior art FIG. 3. This shows that, as a practical matter, the material was so destroyed that it was totally unacceptable as a battery separator or enveloping material.
U.S. Pat. No. 3,023,261 discloses a separator coating for alkaline nickel-cadmium cells. In accordance with this disclosure, one would first dip the plate in mixture consisting of a water insoluble synthetic resin (such as, polyvinyl chloride and, copolymers of various acrylonitrile-vinyl chloride compositions and, polyvinyl butyral, cellulose acetate, polyvinyl chloride or polyvinyl acetate) dissolved in a water soluble solvent, and a filler which is water swellable but insoluable in the polymer solvent. Next one would dip the plate in water to extract the solvent from the coating and set the resin.
In evaluating this patent the following examples were prepared in the following manner:
Polyvinyl chloride 100 grams (Geon 140.times.30 by B. F. Goodrich), was dissolved in dimethylformamide (DMF) 600 grams (636 ml). Cornstarch (400 grams) was added to the solution to form a coating mixture. This mixture was filtered through a sieve to eliminate any possible lumps. A dry charge negative electrode was dipped into the mixture for 3 minutes and then pulled out. Photograph prior art FIG. 4 was quickly taken. It shows the air bubbles which will become pin holes. The plate was allowed to soak in water for five minutes. Then the plate was washed in cold water for two hours and air dryed in a 60.degree. C. forced-air oven for one hour.
This plate passed the electrical pin hole test, but still leaked 10 milliamperes of current. The coating showed unacceptably large pin holes as indicated in the photograph of plate BA, prior art FIG. 5.
It passed the electrical pin hole test, due to the great thickness of the coating.
The coating suspension gelled on standing for a few hours which made it unusable for purposes of dipping; the solvent having swelled the water swellable filler.
Polyvinyl butyral, by Aldrich Chemical Co., 7.5 was dissolved in methyl alcohol 120 grams. Then 45 grams of carboxyethyl cellulose, by Hercules, was added and the mixture mixed under high shear. A negative electrode was dipped into the coating suspension for three minutes and then immersed into water for five minutes. A photo was taken, prior art FIG. 6. It shows that no significant coating resulted. Then the plate was washed in water for two hours and labeled as plate BC.
Polyvinylidene chloride, Saran Resin F-310 by Dow Chemical, 13.4 grams was dissolved in 108 grams of DMF (Dimethylformamide). Then 40 grams of polyvinyl alcohol, Gelvatol 20-30 by Monsanto, was blended in at high shear for three minutes. A negative dry charged plate was immediately dipped into the coating mixture for three minutes and then dipped into water for five minutes followed by washing in cold water for two hours. The plate was air dryed in a 60.degree. C. oven for 30 minutes. A photo was taken, prior art FIG. 7, of the plate identified as BD. Again, as will be noted, the pin holes are unacceptable from a commercial battery separator standpoint. Furthermore, this coating suspension also gelled and became unusable after a few hours.
Cellulose acetate (CA-398-3 by Eastman Kodak) 20 grams was dissolved in 150 grams of acetone. Zein (62.5) was undippable so it was placed in a blender at high speed for three minutes. A dry charge plate was dipped for three minutes and then immersed in water for five minutes, followed by washing in cold water for two hours. The plate was dryed in a 60 degrees C. oven for 10 minutes. The plate BB, prior art photo FIG. 8, indicates commercially unacceptable pin holes due to air bubbles.
The results of the cycle tests are described in Table II.
TABLE II __________________________________________________________________________ INITIAL VOLTAGE FINAL VOLTAGE INITIAL AMPERAGE FINAL AMPERAGE CYCLE # CYCLE # CYCLE # CYCLE # LOUIS PLATE # 1 2 3 1 2 3 1 2 3 1 2 3 EXAMPLE __________________________________________________________________________ # BA 1.0 1.25 1.25 0.5 0.55 0.55 24 32 30 14 14 16 3 BB 0.3 0.30 0.35 0.23 0.25 0.27 8 8 12 6 6 12 8 BC 0.0 0.0 1.5 0.0 0.0 0.75 0 0 45 0 0 24 5 BD 1.18 1.35 1.37 1.05 0.65 0.75 36 36 40 14 18 24 6 CONTROL 1.32 1.45 1.40 0.75 0.85 0.77 37 40 42 20 24 26 __________________________________________________________________________
Results of this test show that the material not only did not provide an acceptable separator material because of the inclusion of unacceptable pin holes, but also did not provide an acceptable envelope material because of the close adherence of the material to the plates which depressed electrical performance due to electrolyte starvation.
U.S. Pat. No. 779,553 issued Jan. 10, 1905 discloses the use of a first coat applied to a plate which dissolves in the battery electrolyte leaving a second coat as a sheath. This process can be referred to as "leaching". In accordance with the disclosure, the first caot is a syrup formed of lump sugar or saccharose dissolved in water. The second coat is applied by dipping in a solution comprised of, for example, tetra acetate of cellulose or a solution of tetra acetate of cellulose and tetra butyrate of cellulose or a solution of tetra butyrate of cellulose or a solution of castor-oil, essence of turpentine and nitrate of cellulose.
In testing the disclosure of this patent, the following solutions were prepared:
The cellulose acetate and cellulose-acetate butyrate were from Eastern Kodak and are respectively known as CA398-3 and CAB381-0.5.
__________________________________________________________________________ COMBINATIONS TRIED SUGAR PLASTIC PLASTIC PLATE AA SUGAR SOAK AIR COATING SOAK # L M H Time DRIED Type SOLVENT Time __________________________________________________________________________ AA -- -- X 10 min. Yes CA THF 30 min. AB -- X -- 24 hrs. No CA THF 30 min. AC -- X -- 5 min. No CAB THF 30 sec. AD -- X -- 5 min. No CA MEK 30 sec. AE X -- -- 10 min. No CA THF 30 sec. AF X -- -- 30 min. No CAB MEK 30 sec. __________________________________________________________________________ CA = Cellulose Acetate CAB = Cellulose Acetate Butyrate L = Light M = Medium H = Heavy THF = Tetrahydrofuran MEK = Methylethylketone
Typical procedure:
Plate immersed in sugar solution for 10 minutes then immediately dipped into plastic solution for 1/2 minute followed by air-drying.
Typical results:
There was inadequate wetting of plate by the sugar solution. There was bubble formation upon dipping the plate into the plastic solution and then pinhole formation upon drying the plate.
The cellulose acetate film dissolved in battery acid after soaking at room temperature for less than 24 hours.
All the plates had pinholes. This was indicated visually and with an electronic pinhole test.
The Electronic Pinhole Test was as follows:
The coated plate was placed on a metal stand. Then a potential of one kilo volt AC is applied between the stand and plate. If more than 15 milliamperes passes through the coating, a pinhole was present.
The plates were charged for 10 hours and allowed to stand on open circuit. Each cell was discharged across a 0.1 or 0.5 ohm resistor for one minute. The initial and final voltages and amperages were recorded. Three charge, discharge cycles were performed. The experimental plates were labeled AA thru AE, (see Table III). The separators AA thru AE disintegrated, except for the control cell, which had a paper separator.
TABLE III __________________________________________________________________________ INITIAL VOLTS FINAL VOLTS INITIAL AMPERES FINAL AMPERES CYCLE # CYCLE # CYCLES I CYCLES II PLATE # 1* 2 3 1* 2 3 1* 2 3 1* 2 3 __________________________________________________________________________ AA* 1.25 0 .15 1.3 0 0 12.5 0 16.0 11.5 0 0 AB* 1.4 0 0 1.0 0 0 14.0 0 0 10.0 0 0 AC .75 .45 0 .45 0 0 7.5 9 0 4.5 0 0 AD .2 .75 0 .15 0.32 0 2 12 0 1.5 6.4 0 AE 0.1 1.15 0 0.1 0.55 0 1.0 23 0 1.0 10.6 0 Control 1.5 1.25 1.25 1.3 .72 .70 13.2 21 16.0 12.2 14.4 10 __________________________________________________________________________ *Discharged with a 0.1 ohm resister. In all subsequent discharge cycles a 0.5 ohm resister was used.
Initially, plates AA and AB gave better results than AD and AE, while plate AC was intermediate. This is because plates AA and AB had coatings, which dissolved in the battery acid and in effect approached being no separator at all. Plates (AD and AE) had coatings, which did not immediately dissolve in the battery; but completely insulated the plate and kept it from conducting electricity. On the second discharge, plates AA, AB, and AC indicated a shorting-out of the plates. On the other hand, plates AD, AE and AF began to lose their coatings, which enabled them to conduct electricity. On the third and last discharge, all the coated plates had electrical discharge curves similar to shorted-out plates. On inspection all the coated plates had lost their coating. The photographs, prior art FIGS. 9 through 17, clearly illustrate the before and after conditions of the plates.
Plates AG and AH were prepared in the following manner:
Cellulose nitrate, by Hercules Grade RS 1/2, 80 grams was dissolved in 200 milliliters of THF (Tetrahydrofuran) then 8 milliliters of castor oil was blended into the solution. A negative lead electrode was soaked in a light sugar solution "G" for 20 minutes. Then the plate was immediately immersed in the solution for three minutes and allowed to air dry. A photo was taken, prior art FIG. 18, and then the plate was labeled AG. Once again, air bubbles formed upon immersion. Cellulose nitrate did not dissolve in turpentine as suggested in the patent. Cellulose nitrate, by Hercules Grade RS 1/2, 80 grams was dissolved in 200 milliliters of ethyl acetate, then 8 milliliters of castor oil was blended into the solution. A negative lead electrode was soaked in a light sugar solution "G" for 20 minutes. Then, the plate was immediately immersed in the solution for three minutes and allowed to air dry. A photo was taken, prior art FIG. 19, and the plate labeled AH. Once again, air bubbles formed upon immersion.
Of all the plastics tried, in this patent, only cellulose acetate (i.e. tetra acetate of cellulose) was unstable in battery acid. However, cellulose-acetate butyrate was unstable when placed between two electrodes and placed on charge.
The cellulose nitrate when placed on charge and cycled was flawed because it had pinholes and electrically insulated the plate.
These tests show that this patent, like the others tested, did not produce by one or more dippings in a variety of coatings and compositions, an acceptable battery separator material on the plate or about the plate in the form of an envelope. Thus, the prior art taken either alone or in combination does not show a method of providing by a dip process an acceptable separator material about an electrode nor the product produced by such a method.